Piriformospora indica is an endophytic fungus of Sebacinaceae which colonizes the roots of many plant species and confers benefits to the hosts. We demonstrate that approximately 75% of the genes, which … respond to P. indica in Arabidopsis roots, differ among seedlings grown on normal phosphate (Pi) or Pi limitation conditions, and among wild-type and the wrky6 mutant impaired in the regulation of the Pi metabolism. Mapman analyses suggest that the fungus activates different signaling, transport, metabolic and developmental programs in the roots of wild-type and wrky6 seedlings under normal and low Pi conditions. Under low Pi, P. indica promotes growth and Pi uptake of wild-type seedlings, and the stimulatory effects are identical for mutants impaired in the PHOSPHATE TRANSPORTERS1;1, -1;2 and -1;4. The data suggest that the fungus does not stimulate Pi uptake, but adapts the expression profiles to Pi limitation in Pi metabolism mutants.
Piriformospora indica, an endophytic root-colonizing fungus, efficiently promotes plant growth and induces resistance to abiotic stress and biotic diseases. The fungal cell wall extract induces cytoplasmic … calcium [Ca2+]cyt elevation in host plant roots. Here, we show that an elici-tor-active cell wall moiety, released by P. indica into the medium, is cellotriose (CT). CT in-duces a mild defense-like response including the production of reactive oxygen species, changes in membrane potentials and the expression of genes involved in growth regulation and root development. CT based [Ca2+]cyt elevation in Arabidopsis roots does not require BAK1 coreceptor, or the putative Ca2+ channels TPC1, GLR3.3, -2.4 and -2.5 and operates synergistically with the elicitor chitin. We identified an ethylmethane-sulfonate-induced mu-tant ([Ca2+]cyt elevation mutant, cycam) impaired in response to CT, cellooligomers (n = 2, 4-7), but not to chitooligomers (n = 4-8) in roots. The mutant contains a single nucleotide ex-change in the gene encoding for a poly(A) ribonuclease (AtPARN, At1g55870) which de-grades poly(A) tails of specific mRNAs. The wild-type PARN cDNA, expressed under the control of a 35S promoter, complements the mutant phenotype. Our finding of cellotriose as a novel chemical mediator might help to understand the complex P. indica-plant mutual rela-tionship in beneficial symbiosis.
Authors: J. M. Johnson, J. Thurich, E. K. Petutschnig, L. Altschmied, D. Meichsner, I. Sherameti, J. Dindas, A. Mrozinska, C. Paetz, S. S. Scholz, A. C. Furch, V. Lipka, R. Hedrich, B. Schneider, A. Svatos, R. Oelmuller